Japanese Patent Application Publication No. 2016-162897 describes a semiconductor device including a diode structure. This semiconductor device includes a semiconductor substrate, an upper electrode provided on an upper surface of the semiconductor substrate, and a lower electrode provided on a lower surface of the semiconductor substrate located opposite to the upper surface. The semiconductor substrate includes a p-type anode region being in contact with the upper electrode, an n-type cathode region being in contact with the lower electrode, and an n-type drift region having a carrier density lower than a carrier density of the cathode region and interposed between the anode region and the cathode region.
This semiconductor device further includes an n-type barrier region interposed between the anode region and the drift region, and an n-type pillar region being in Schottky contact with the upper electrode and extending between the barrier region and the upper electrode. A carrier density of the barrier region is higher than the carrier density of the drift region. According to this configuration, since injection of holes from the anode region to the drift region is suppressed at forward bias, a recovery current occurring upon switching to reverse bias can be reduced.
Meanwhile, the presence of the aforementioned barrier region and pillar region may be a factor causing a snapback phenomenon in which an increase in a forward current temporarily delays relative to an increase in a forward voltage upon switching to the forward bias. In order to suppress the snapback phenomenon, the barrier region may have a low carrier density. However, when the carrier density of the barrier region is low, the aforementioned effect of suppressing the hole injection is reduced. In this regard, in the semiconductor device of Japanese Patent Application Publication No. 2016-162897, the carrier density of the barrier region is varied along a lateral direction of the semiconductor substrate (i.e., a direction parallel with the semiconductor substrate). According to this configuration, the barrier region can suppress the hole injection by its portion having a high carrier density and can also suppress the snapback phenomenon from occurring by its portion having a low carrier density.